Śrīla Bhaktivinoda Ṭhākura points out that there are thirty-five items up to the point of observing special vows in the month of Kārttika. To these thirty-five items, another four are added — namely marking tilaka on different parts of the body, writing the names of the Lord all over the body, accepting the Deity’s garland and accepting caraṇāmṛta. These four items are understood to be included by Kavirāja Gosvāmī within arcana, worship of the Deity. Although these items are not mentioned here, they are to be added to the previous thirty-five items. Thus the total number becomes thirty-nine. To these thirty-nine should be added five others: association with devotees, chanting the Hare Kṛṣṇa mahā-mantra, reading Śrīmad-Bhāgavatam regularly, residing in Mathurā, the birthplace of Kṛṣṇa, and worshiping the Deity with great respect and veneration. The thirty-nine items plus these five come to a total of forty-four. If we add the previous twenty items to these forty-four, the total number becomes sixty-four. The five items mentioned above repeat previously mentioned items. In the Bhakti-rasāmṛta-sindhu, Śrīla Rūpa Gosvāmī states:

aṅgānāṁ pañcakasyāsya pūrva-vilikhitasya ca
nikhila-śraiṣṭhya-bodhāya punar apy atra śaṁsanam

“The glorification of these five items [association with devotees, chanting the holy name and so on] is to make known the complete superiority of these five practices of devotional service.”

The sixty-four items of devotional service include all the activities of the body, mind and senses. Thus the sixty-four items engage one in devotional service in all respects.